Granular n-substituted polyamides



l polyamides.

Patented Nov. 18, 1947 GRANULAR N -SUBSTITUTED POLYAMIDES Alban T.Hallowell and Henry -D. Foster, Wilmington, Del.,

and Arthur W. Larchar, Mendenhall, Pa., assignors to E. I. duPont de Ne-.mours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application February 9,1944,

Serial No. 521,660

This invention relates to polymeric materials and particularly toimprovements in the manufacture of modified polyamides in granular form.

The polyamides with which this invention is concerned are of the generalkind described in U. S. Patents 2,071,250, 2,071,253 and 2,130,948, inwhich the average number of carbon atoms in the segments of the chainseparating the amide T. L, Cairns, S. N. 445,635, filed June 3, 1942,and

S. N, 507,745, filed October 26, 1943, and also in the copendingapplications of H. D. Foster and A. W. Larehar, S. N. 503,130, filedSeptember 20, 1943, and Serial No. 521,659, .filed February 9. 1944. Thepresent invention provides further improvements in the methods ofisolating the N-alkoxymethyl polyamides in finely divided granular form.

In the condensation of a polyamide with an aldehyde and an alcohol, theresinous product obtained generally contains both alkoxymethyl and 9Claims. 260-72) methylol groups substituted for. the carbonamidehydrogens initially present in the resin. When an acid-reactingcondensation catalyst is employed in the reaction between a polyamide,an

this small amount of unetherified methylol groups aldehyde and analcohol, especially if the alcohol an improved process for themanufacture of N- alkoxymethyl polyamides in granular form. Anotherobject is to provide more precise control over the method of granulatingN-alkoxymethyl polyamides than has been possible hitherto. A furtherobject is to provide a process for pretreating N -alkoxymethylpolyamides, whereby less mechanical working will-be required to producethe desired granulation.

These and other objects are accomplished in accordance with thisinvention by reducing the methylol content of N-alkoxymethyl polyamidesto below about 0.4% prior to granulation. The selective removal ofmethylol groups from N-alkoxymethyl polyamides which contain N-methylolgroups may be effected as described in the copending application S. N,507,745 of T. L. Cairns, filed October 26,1943.

In a preferred embodiment of the present invention, an N-alkoxymethylpolyamide, made by acid condensation of a polyamide with formaldehydeandan alcohol, and containing several,

tenths of a, per cent of methylol groups, is treated, prior togranulation, with an aqueous or an alcoholic solution of a reagent suchas a water-soluble sulfite, hydroxide, or carbonate of an alkali metalor alkaline earth metal, whereby the methylol content of the resin isreduced to below 0.4%.

Reduction of the methylol content can be achieved alsoby prolongedstorage of the resin in an alcoholic ammonia. solution. The solution ofN-alkoxymethyl polyamide, after the treatment for removal of methylolgroups is mixed with sufficient Water to cause precipitation of theresin as a resin-containing slimy fluid, which, upon working in a doughmixer with additional quantities of water, yieldsiirst a stiffenedresinous mass, and then a dispersion of fine solid particles.

The condensation of polyamide with formaldehyde and alcohols may beeffected by treating a polyamide, such as polyhexamethylene adipamide,with an excess of formaldehyde and an alcohol in the presence of an acidcatalyst, suitably with agitation in a closed vessel at 100 to 150 C.Phosphoric acid is the preferred acidreacting catalyst. The amount ofcatalyst should 'be about 1 to 10% of the weight of polyamide interfereswith the granulation of alkoxym'ethyl The granulation is generallyconducted by precipitating the resin from solution in a water-misciblesolvent by addition of water under carefully controlled conditions,followed by mechanical working of the precipitated resin in the presenceof water.

An object of the present invention is to provide used. Other suitablecatalysts includ formic,

' acetic, oxalic, trimethyl acetic, benzoic, sulfuric,

p-toluenesulfonic, hydroxyacetic and maleic acids. The preferredprocedure is as follows: 1 part polyamide, 0.8 to 1.5 parts offormaldehyde, and

1.0 to 2.0 parts of methanol are charged into a pressure vessel equippedwith an agitator. The

-mixture is heated toa temperature of to C., and 0.03 to 0.05 part ofphosphoric acid (85%) is injected rapidly to seconds). After a reactiontime of about 15 minutes or less (prefer-'- ably 8 to 12 minutes), thereaction mixture is forced out of the reaction vessel into a quenchingbath which preferably is an aqueous alcohol solution containingsufficient alkaline reagent, such as ammonia, to neutralize thephosphoric acid. As an example, a satisfactory quenching medium maycontain about 2.6 parts of methanol, 0.8 part of water and 0.08 part 28%aqueous ammonia per part of polyamide. The resulting mixture is cooledto about room temperature, and then freed of solid impurities byfiltration or centrifuging. The solution obtained in this manner may betreated directly with a, reagent for removal of N-methylol groups fromthe resin, or the resin may first be isolated by precipitation withwater, and subsequently treated in the form of an aqueous slurry withthe N-methyiolremoving agent.

A convenient method for isolating the N- alkoxymethyl polyamides ingranular form is by treating the solution of N-alkoxymethyl polyamidewith water to precipitate a resin-containing fluid, agitating this fluidwith aqueous sodium hydroxide or other N-methylol-removing reagent, andworking the resulting product mechanically in the presence of wateruntil the resin stiffens and ultimately breaks up in fine granular form.As an example, the solution of N- alkoxymethyl polyamide, prepared asdescribed above, is poured into a relatively large volume of waterwhereby a resin-containing fluid layer precipitates. This fluid isallowed to stand for 24 hours under water, and is thereafter transferredto a dough mixer where it is worked with water formaldehyde in 52 partsof methanol for 30 parts of ice and 189 parts of water.

neutralizing the mixture with ammonia, the

for about 30 minutes to remove unreacted alcohol 1 and aldehyde. Theresulting doughy mass is worked with a 1% sodium hydroxide solution for15 minutes at 50 C.,wherebygranu1ation occurs, usually in about one-halfto two hours. The resulting resin is found to have a methylol content of0.1%. Without the sodium hydroxide treatment the resin contains 0.5 to0.7% of methylol.

The treatment for removal of N-methylol groups results in economies inthe granulation operation by reducing the amount of mechanical workingwhich is necessary to produce the granulation. The time required for thegranulation, it is now discovered, increases with the methylol content.Thus, if the polymer contains less than 0.2% of methylol, it can begranulated by working in dough mixer in the presence of water for abouttwo hours or less. The polymers which contain 0.3% of methylol generallyrequire several hours to granulate, and when the methylol contentexceeds 0.4% granulation is diflicult or impossible to achieve by themethods at present available. Hence it is preferred to reduce the N-methylol content to 0.2% or lower. a

It is, of course, also desirable to remove the N-methylol groupsselectively, i. e. without simultaneous destruction of theN-alkoxymethyl groups. Prolonged treatment with the methylolremovingagent at high temperature is therefore to be avoided.

The invention is further illustrated by the folhexamethylene adipamidein about 35 parts of 90% formic acid and 78 parts of acetic anhydridewas rea ted with a solution of parts of paraminutes at a temperature of65 to 70 C. Approximately 71 parts of methanol were added during thisperiod. The resulting reaction mixture was poured into 450 parts ofacetone, 450 After polymer mass was withdrawn and washed for one hourwith water in a dough mixer. To this 2.8 parts of sodium sulflte wasadded and worked with the resin for 20 minutes. Thereafter the mixturewas heated to 90 C. for 1 hour, after which the polymer was washed freeof sulfite. Upon further working in the mixer, the polymer broke up intofine solid particles which could be hardened by treatment with coldwater.

Example II.In a steam jacketed, nickel-lined autoclave was placed '70parts of polyhexamethylene adipamide cut to pass a screen, 70 partsparaformaldehyde, and 107.5 parts of methanol. This mixture was heatedwith agitation to 139 C. and a solution of 1 part of methanol and 2.5parts of phosphoric acid was injected rapidly (10-15 seconds). Thereaction mixture was held at 139 C. for 8 minutes after the addition ofthe catalyst and was then discharged rapidly into a solution containingparts methanol, 56 parts of water, and 5.6 parts 28% aqueous ammonia.The resulting solution was cooled and filtered to remove a small amountof solid matter. A sample of the resin was isolated by precipitationwith water followed by washing and drying. It had a methoxyl content of10.4% and a methylol content of 0.51%, corresponding to a total amidesubstitution of about 48%. The solution thus prepared was used in theexamples which follow.

(A) A portion of the solution prepared as described above was stored atroom temperature for '7 days. It was thereafter treated with hot waterin suflicient quantity to precipitate the resin as a slimy fluid. Thelatter was worked for 70 minutes with water at 21 C. in a dough mixer,after which it began to assume a spongy, somewhat cellular structure.Further working for about 2 hours caused the mass to break up completelyinto small granules. These were separated from the mother liquor bycentrifuging and washing. After being dried the granular resin was foundto have a methylol content of 0.26%.

(B) A portion of the solution prepared as described above was held for16 hours at a temperature of 50 to 60 C. The resin was then precipitatedas a slime and worked in a dough mixer with water at 30 to 32 C. Agranular product was obtained after working for 4 hours in the mixer(methylol content, 0.3%).

Similar treatment of the solution without the preheating treatment gavea resinous mass which would not granulate even after 8 hours mixing.

(C) Two hundred parts of solution prepared as described above was pouredwith agitation into 1500 parts of 1.6% NaOH solution. After 13 minutesthe resin mass .was removed from the alkaline precipitation liquor andworked with water at 31 to 33 C. in a dough mixer. At the end of twohours, the resin had broken up into small granules. Its methylol contentwas 0.10%.

Example III .-A mixture containing 70 parts of polyhexamethyleneadipamidc, 70 parts of formaldehyde, and 107.5 parts of methanol washeated to C. At that temperature a mixture containing 1 part of methanoland 2.5 parts of 85% phosphoric acid was injected, and the resultingcondensation reaction was permitted to take place for a period of 8minutes, after which the mixture was discharged into a quench liquorcontaining 128 parts of methanol, 56 parts of water and 3.35 parts ofsodium hydroxide. The crude quench liquor contained a fine precipitateof sodium phosphate, and in consequence filtered rather slowly. Thesodium hydroxide reacted with the resin to reduce the methylol contentand the resin was isolated from the resulting filtrate as a slime byprecipitation with hot water, and was worked in a dough mixer with waterat a temperature of 28 C. The resin granulated nicely after working in amixer for 2 hours. The finished product contained 0.11% methylol and10.3% methoxyl.

The polyamides which may be treated by the general method describedabove include polyhexamethylene adipamide, polyhexamethylene sebacamide,and polyamides derived from epsilonaminocaproic acid. In general,polyamides are linear synthetic resins having a recurring II I group (Xbeing oxygen or sulfur). Interpolymers of such polyamides also may beused. In the preparation of N-alkoxymethyl polyamides, alcohols ingeneral condense with formaldehyde and the polyamide, suitable alcoholsbeing methanol, ethanol, isopropanol, n-propanol and allyl alcohol. Itis not necessary, although it is usually preferred to use the samealcohol in the quenching bath as in the condensation mixture.

The granular N-alkoxymethyl polyamides prepared in accordance with thisinvention are useful in the manufacture of molded products, foils,filaments, bristles, coatings, self-sealing fuel cells, electricalinsulation and the like.

It is to be understood that many apparently different embodiments of thepresent invention may be made without departing from the spirit andscope thereof, and that accordingly we do not limit ourselves, except asset forth in the appended claims.

We claim:

1. In a process for preparing granular N-alkoxymethyl polyamides, thesteps which comprise reacting, with an aqueous solution of an alkalinereagent of the class consisting of ammonia, alkali metal hydroxides, andalkali metal sulfites, a substituted polyamide containing N-alkoxymethylsubstituents and more than 0.4% by weight of N-methylol substituents,said polyamide prior to substitution being a linear polymer, havingrecurring intralinear carbonamide groups along the chain, the averagenumber of carbon atoms in the segments of the chain separating the amidegroups being at least two, continuing the said reaction until theN-methylol content of the said substituted polyamide is reduced to below0.4%, and thereafter. granulating the resulting resin by adding water toa solution thereof in a monohydric alkanol having not more than threecarbon atoms per molecule, and mechanically agitating the resultantprecipitate in the presence of water.

2. In a process for preparing granular N-alkoxymethyl polyamides thesteps which comprise reacting with reagent of the class consisting ofammonia, alkali metal hydroxides and alkali metal sulfites, thesubstituted polyamide containing N-alkoxymethyl substituents and morethan 0.4% by weight of N-methylol substituents, said polyamide prior tosubstitution being a linear polymer having recurring intralinearcarbonamide groups along the chain, the average number of carbon atomsin an aqueous solution of an alkaline the segments of the chainseparating the amide groups being at least two, continuing the saidreaction until the methylol content of the said substituted polyamide isreduced to below 0.2%, and thereafter granulating the resultantN-alkoxymethyl polyamide by adding water to a solution thereof in amonohydric alkanol having not more than three carbon atoms per molecule,whereby a precipitate is formed, and mechanically agitating the saidprecipitate in the presence of water.

3. The process set forth in claim 2 in which the alkali metal hydroxideis sodium hydroxide.

4. The process set forth in claim 2 in which the alkaline reagent issodium sulflte.

5. In a process for preparing granular N- alkoxymethyl polyamides, thesteps which comprise reacting with a dilute aqueous solution of alkalimetal hydroxide a polyamide containing -a1koxymethyl substituents andN-methylol substituents, the methylol content being greater than 0.4said polyamide being a linear polymer having recurring intralinearcarbonamide groups along the chain, the average number of carbon atomsin the segments of the chain separating the amide groups being at leasttwo, while mechanically agitating the resulting reaction mixture,whereby the methylol content of the said alkoxymethyl polyamide isreduced below 0.4% and granulation of the N-alkoxymethyl polyamideoccurs.

6. The process set forth in claim 5 in which the -alkoxymethyl polyamideis N-methoxymethyl polyhexamethylene adipamide.

7. A process for preparing granular N-alkoxymethyl polyamides whichcomprises heating at a reaction temperature in the range of to C., inthe presence of 1% to 10% by weight of an acid catalyst of the classconsisting of phosphoric, formic, acetic, oxalic, trimethyl acetic,benzoic, sulfuric, p-toluenesulfonic, hydroxyacetic, and maleic acids, areaction mixture of one part polyamide, 0.8 to 1.5 parts of formaldehydeand 1.0 to 2.0 parts of methanol, said polyamide being a linear polymerhaving recurring intralinear carbonamide groups along the chain, theaverage number of carbon atoms in the segments of the chain separatingthe amide groups being at least two, quenching the resulting reactionmixture after a reaction time of from 8 to 15 minutes in an aqueousmethanol solution containing sufficient ammonia to neutralize the saidacid catalyst, mixing Water with the quenching solution whereby aprecipitate of N -alkoxymethyl polyamide is formed, stirring the saidprecipitate with an aqueous solution of an alkaline reagent of the classconsisting of ammonia, alkali metal hydroxides, and alkali metalsulfites, until the methylol content of the N-alkoxymethyl polyamide isreduced to below 0.4% by weight, granulating the resultingN-alkoxymethyl polamide by mechanically agitating it in the presence ofwater, and separating the said granulated N-alkoxymethyl polyamide fromthe aqueous liquid associated therewith.

8. A process for preparing granular N-alkoxymethyl polyamides whichcomprises heating at a reaction temperature in the range of 100 to 1500., in the presence of 1% to 10% by weight of an acid catalyst of theclass consisting of phosphoric, formic, acetic,-oxalic, trimethylacetic, benzoic, sulfuric, p-toluenesulfonic, hydroxyacetic, and maleicacids, a reaction mixture of one part polyamide, 0.8 to 1.5 parts offormaldehyde and 1.0 to 2.0 parts of methanol, said polyamide being alinear polymer having recurring intralinear carbonamide groups along thechain, the average number of carbon atoms in the segments of the chainseparating the amide groups being at least two, quenching the resultingreaction mixture after a reaction time of from 8 to 15 minutes in anaqueous methanol solution containing sufiicient sodium hydroxide toneutralize the said acid catalyst, mixing water with the quenchingsolution whereby a precipitate of N-alkoxymethyl polyamide is formed,stirring the said precipitate with an aqueous solution of an alkalinereagent of the class consisting of ammonia, alkali metal hydroxides, andalkali metal sulfites, until the methylol content of the N-alkoxymethylpolyamide is reduced to below 0.4% by weight, granulating the resultingN-alkoxymethyl polyamide by mechanically agitating it in the presence ofwater, and separating the said granulated N- alkoxymethyl polyamide fromthe aqueous liquid associated therewith.

9. A process for preparing N-methoxymethyl polyamides which comprisesheating at a reaction temperature in the range of 100 to 150 C. areaction mixture of one part polyamide, 0.8 to 1.5 parts formaldehyde,and 1.0 to 2.0 parts of methanol, said polyamide being a linear polymerhaving recurring intralinear carbonamide groups along the chain, theaverage number of carbon atoms in the segments of the chain separatingthe amide groups being at least two, introducing into this mixture atthe said reaction temperature 0.03 to 0.05 part of 85% phosphoric acid,quenching the resulting mixture after a reaction time of 8 to 15 minutesin an aqueous methanolic solution containing sufflclent ammonia toneutralize the phosphoric acid, mixing water with the quenched solutionwhereby a precipitate containing N-methoxymethyl polyamide is formed,stirring the said precipitate with an aqueous solution of alkali metalhydroxide, until the methylol content of the resin is reduced below 0.4%by weight, granulating the resulting N-alkoxymethyl polyamide bymechanically agitating it in the presence of water, and separating thesaid granulated N-alkoxymethyl polyamide from the aqueous liquidassociated therewith.

ALBAN T. HALLOWELL.

HENRY D. FOSTER.

ARTHUR W. LARCHAR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,244,184 Austin et al June 3,1941 2,173,005 Strain Sept. 12, 1939 FOREIGN PATENTS Number Country Date542,128 Great Britain Dec. 29, 1941 OTHER REFERENCES Ephraim-InorganicChemistry, 4th ed. (1943), Nordeman Publishing Co., Inc., N. Y., pages801-11.

